1. Field of the Invention
This invention relates to an apparatus for processing television camera signals used in close circuit television for recording and monitoring system.
2. Description of the Prior Art
In a monitoring television system used, as one of information transmission systems, at least one video cassette recorder or a digital video recorder is connected through an electronic switch to a plurality of television cameras and transmission lines. The electronic switch provides for a fast rate sequential switching for recording onto the video recorder a picture image of one camera after another.
In such an information transmission system, it is preferable to mutually lock the internal synchronizing signals of a plurality of television cameras and the electronic switching time to an external synchronizing signal, in order to prevent the recording from being disturbed during and immediately after the switching operation from one television camera to another.
A known apparatus for synchronizing a plurality of television cameras is an apparatus for transmitting an external synchronizing signals from an external synchronizing generator to the television cameras by injecting the external synchronizing signal into the video signal transmission line and locking an internal synchronizing signal generator of the television camera by means of the transmitted external synchronizing signal. Such an apparatus is disclosed in U.S. Pat. No. 4,603,352 the contents of which are incorporated herein by reference.
Another known apparatus for synchronizing the plurality of the television camera signals is an apparatus for memorizing each of the television camera signal in a memory circuit and feeding the signals to the video recorder, synchronously via the electronic switch from the memory circuits. Such an apparatus is disclosed in U.S. Pat. No. 5,267,039 the content of which are incorporated herein by reference.
Furthermore, the known apparatuses for recording a plurality of camera signals at fast sequencing rate require that each individual camera signal will incorporate coded identification signals, providing for a simple retrieval of the signal through a coded selection. In the case of using analog video cassette recorder, the coded identification is known to be recorded during the vertical blanking period of the television signals, but in the case of using a digital video recorder it is known that digital video recorders ignore the vertical blanking period and instead they employ a complex control software for indexing the files of the recorded digital signals of each individual camera.
Because the software programs for controlling the individual files of the digitally recorded camera signals are complex, it renders the processing, transferring and/or retrieval of the recorded digital signals to and from disks, tapes or other medium time consuming. Moreover, because of the limited capacity of the digital recorder's storage medium the digital video recorders record in a continuous FIFO (First In First Out) rotation, and it is necessary to introduce protection software programs for the recorded alarms or event files in order to retain such recording for extended periods by excluding such alarms and events files from the FIFO process. The continued randomly changing, deletion and/or addition of protected files causes an extremely complex and inefficient FIFO recording in rotation, particularly when large numbers of television cameras are used. Moreover, the complexity of the software programs makes it literally impossible to combine plurality of digital recorders for increasing the overall storage capacity.
In another known digital recording system, a plurality of camera signals are processed in parallel instead of being sequentially switched and are stored in individual files within the digital recorder storage medium, but due to the limited storage capacity the recording is also processed in FIFO rotation and similar file protection software programs are necessary. The complexity of such programs for managing large number of files in the FIFO rotation and the continuous changes and addition to the protection files makes the software for the system management laborious, costly and inefficient. Here too the complexity of the software programs along with the plurality of input connectors makes it literally impossible and/or prohibitively expensive to interconnect and/or combine multiple digital recorders in order to increase the overall storage capacity.